Understanding the Mode of Action of ThDP in Benzoylformate Decarboxylase

The mechanism of all elementary steps involved in the catalytic cycle of benzoylformate decarboxylase (BFD, E.C. 4.1.1.7) to generate the acyloin linkage is investigated by extensive molecular dynamics simulations. Models involving different charge states of amino acids and/or mutants of critical residues were constructed to understand the involvement of the catalytically active residues and the reactivity differences between different substrates in this reaction. Our calculations confirm that H70, S26, and H281 are catalytically active amino acids. H281 functions as a base to accept H-donor in the first nucleophilic attack and as an acid in the second, to donate the proton back to O-acceptor S26 assists H281 in deprotonation of the donor aldehyde and protonation of the acceptor aldehyde. In both the first and second nucleophilic attacks, H70 interacts with O-aldeltyde and aligns it toward the nucleophilic center. H70 has been found to have an electrostatic effect on the approaching aldehyde whose absence would block the initiation of the reaction. The reactivity difference between benzaldehyde (BA) and acetaldehyde (AA) is mainly explained by the steric interactions of the acceptor aldehyde with the surrounding amino acids in the active center of the enzyme. (C) 2009 Wiley Periodicals, Inc. Biopolymers 93: 32-46, 2010.